在 FireFox 中,如果使用 document.getElementById('obj'); 那么你的元素一定要指定 id 属性!而不仅仅指定 name 属性 <html> 
<body> 
    <form id="form1" runat="server"> 
    <div> 
        <input type="checkbox" name="chk1" id="chk1"  /> 
        <asp:Button ID="Button1" runat="server" Text="Button" /> 
    </div> 
    </form> 
</body> 
</html> 
<script language="javascript" type="text/javascript">             document.getElementById(" <%=Button1.ClientID %>").disabled = true; 
            
            document.getElementById("chk1").onclick=function(){ 
                if(document.getElementById("chk1").checked){ 
                    document.getElementById(" <%=Button1.ClientID %>").disabled = false; 
                }else{ 
                    document.getElementById(" <%=Button1.ClientID %>").disabled = true; 
                } 
            } 
      
</script>